Retinal ganglion cells die in a variety of optic nerve diseases, the most prevalent of which is glaucoma. Previous studies conducted by the investigator and others showed that ganglion cells died in experimental glaucoma and other models of optic nerve disease with characteristics of a form of programmed cell death known as apoptosis. This form of cell death is genetically controlled and it is likely that a better understanding of the genes that regulate this process in ganglion cells will lead to better treatments that can be used to block the death process. This proposal is aimed at determining the role of three genes in the regulation of ganglion cell death. These genes, p53, bcl-x, and bax, appear to form a molecular switch that acts as one of the early control steps in regulating apoptosis in a variety of cell types. Early work has shown that these genes are expressed in ganglion cells. One set of specific aims in this proposal is to determine, using a combined quantitative and localization study, if the expression of these genes in ganglion cells is altered in a fashion predicted by the molecular switch hypothesis (e.g., that p53 expression increases causing a decrease in bcl-x expression and an increase in bax expression). The remaining specific aims involve direct tests of the functions of these genes in the ganglion cell death process. These direct tests will be carried out on genetically altered transgenic mice that have either defective p53 or bax expression or overexpress bcl-x, The basic experimental design of these experiments is to stimulate ganglion cell death in mice using two different approaches (thus the functions of these genes can be tested in diverse pathways leading to ganglion cell death), which include a partial crush of the optic nerve and intravitreal injection of varying doses of the glutamate analog N-methyl-D-aspartate, followed by a quantitative analysis of the rate of cell death.